Liquid crystal displays are attracting attention because of their features such as slimness, lightweight and low power consumption and widely used in portable equipment such as cellular phones and watches, office automation equipment such as personal computer monitors and notebook computers, domestic electrical equipment such as video cameras and liquid crystal televisions, and so on. Laminated films including laminate of retardation films and any of various polarizing plates are used in conventional Liquid crystal displays.
For example, a patent document 1 listed below discloses that a liquid crystal display which has a polarizing plate and a retardation film having a refractive index ellipsoid satisfying the relation nx>nz>ny placed on one side of an in-plane switching (IPS) liquid crystal cell, has improved contrast ratio in oblique directions.
However, liquid crystal displays produced with a conventional laminated film cause a problem. For example, leakage of light or significant changes in color (also referred to as a large amount of color shift) occur depending on the viewing direction, when a black image displayed on a screen is viewed from oblique directions, or optical unevenness is obtained, when backlight is allowed to run for certain hours.
Such a laminated film is generally bonded to a liquid crystal cell with an interposed pressure-sensitive adhesive layer. However, a conventional laminated film causes a problem in which the laminated film is difficult to separate from a liquid crystal cell, or a certain component of the laminated film (such as a retardation film or a pressure-sensitive adhesive layer) is left on the surface of a liquid crystal cell after the process of peeling the laminated film. In general, liquid crystal display undergo inspection before they are shipped. As a result of the inspection, if the laminated film itself is defective or if there is foreign matter between the laminated film and the liquid crystal cell, the laminated film will be separated such that the liquid crystal cell can be recycled (or reworked). Ideally, the laminated film should be bonded to the liquid crystal cell such that peeling or bubbles can be prevented even in a high-temperature, high-humidity environment, while the laminated film should be easily separable from the liquid crystal cell such that the liquid crystal cell can be recycled without causing damage or a change in cell gap. In conventional technologies, it has been difficult to satisfy such conflicting features at the same time. Thus, there have been demands for liquid crystal display panels in which such problems are overcome.
Patent Literature 1: Japanese Patent Application Laid-Open (JP-A) No. 11-305217
The invention has been made in order to solve the problems, and it is an object of the invention to provide a laminated film which may improve the display uniformity in liquid crystal display, and a laminated film which may have both good adhesion to a liquid crystal cell and easy peelability.
As a result of investigations for solving the problems, the inventors have found that the objects can be achieved with the laminated film described below, and have completed the invention.
In an aspect of the invention, a laminated film includes: a polarizing plate; a retardation film; and a first pressure-sensitive adhesive layer, provided in this order. The polarizing plate includes: a polarizer; a first protective layer placed on a side of the polarizer where the retardation film is provided; and a second protective layer placed on another side of the polarizer which is opposite to the side where the retardation film is provided. The retardation film is a stretched film which includes a norbornene resin. The first pressure-sensitive adhesive layer includes a pressure-sensitive adhesive that may be produced by crosslinking a composition which includes a (meth)acrylate (co)polymer and a crosslinking agent comprising a peroxide as a main component.
In a preferred embodiment of the invention, the first protective layer and/or the second protective layer is a polymer film comprising a cellulose resin.
In a preferred embodiment of the invention, the first protective layer is substantially optically isotropic.
In a preferred embodiment of the invention, the first protective layer has a refractive index ellipsoid satisfying the relation nx≈nz>ny, wherein nx is a refractive index in a slow axis direction, ny is a refractive index in a fast axis direction, and nz is a refractive index in a thickness direction;
In a preferred embodiment of the invention, the retardation film has a refractive index ellipsoid satisfying the relation nx>nz>ny, wherein nx is a refractive index in a slow axis direction, ny is a refractive index in a fast axis direction, and nz is a refractive index in a thickness direction;
In a preferred embodiment of the invention, the retardation film has an in-plane retardation (Re[590]) of 80 nm to 350 nm that is measured at 23° C. and a light wavelength of 590 nm.
In a preferred embodiment of the invention, the retardation film has an Nz coefficient of 0.1 to 0.7, wherein the Nz coefficient is calculated from the formula: Rth[590]/Re[590], wherein Re[590] is an in-plane retardation measured at 23° C. and a light wavelength of 590 nm, and Rth[590] is a retardation in a thickness direction that is measured at 23° C. and a light wavelength of 590 nm.
In a preferred embodiment of the invention, the retardation film has an absolute value of photoelastic coefficient of 1×10−12 to 10×10−12 that is measured at 23° C. and a light wavelength of 590 nm.
In a preferred embodiment of the invention, the first pressure-sensitive adhesive layer has an adhesive force (FA) of 2 N/25 mm to 10 N/25 mm at 23° C. to a glass plate, wherein the adhesive force is measured by a process that includes pressing a laminated film with a width of 25 mm against a glass plate by one reciprocation of a 2 kg roller to bond the laminated film to the glass plate, aging the laminate at 23° C. for one hour, and then measuring an adhesive strength when the laminated film is peeled in a 90-degree direction at a rate of 300 mm/minute, wherein the adhesive strength is determined as the adhesive force.
In a preferred embodiment of the invention, the first pressure-sensitive adhesive layer has an anchoring force (FB) of 10 N/25 mm to 40 N/25 mm at 23° C. to the retardation film, wherein the anchoring force is measured by a process that includes pressing a laminate of the pressure-sensitive adhesive layer and the retardation film each with a width of 25 mm against the surface of an indium tin oxide vapor-deposited onto a polyethylene terephthalate film by one reciprocation of a 2 kg roller to bond the laminate to the polyethylene terephthalate film, aging the laminate at 23° C. for one hour, and then measuring an adhesive strength when the polyethylene terephthalate film is peeled together with the pressure-sensitive adhesive layer in a 180-degree direction at a rate of 300 mm/minute, wherein the adhesive strength is determined as the anchoring force.
In a preferred embodiment of the invention, there is a difference (FB−FA) of 5 N/25 mm or more between the anchoring force (FB) of the pressure-sensitive adhesive layer at 23° C. to the retardation film and the adhesive force (FA) of the pressure-sensitive adhesive layer at 23° C. to a glass plate. The anchoring force is measured by a process that includes pressing a laminate of the pressure-sensitive adhesive layer and the retardation film each with a width of 25 mm against the surface of an indium tin oxide vapor-deposited onto a polyethylene terephthalate film by one reciprocation of a 2 kg roller to bond the laminate to the polyethylene terephthalate film, aging the laminate at 23° C. for one hour, and then measuring an adhesive strength when the polyethylene terephthalate film is peeled together with the pressure-sensitive adhesive layer in a 180-degree direction at a rate of 300 mm/minute. The adhesive strength is determined as the anchoring force, and the adhesive force is measured by a process that includes pressing a laminated film with a width of 25 mm against a glass plate by one reciprocation of a 2 kg roller to bond the laminate to the glass plate, aging the laminate at 23° C. for one hour, and then measuring an adhesive strength when the laminated film is peeled in a 90-degree direction at a rate of 300 mm/minute, wherein the adhesive strength is determined as the adhesive force.
In a preferred embodiment of the invention, the (meth)acrylate (co)polymer is a copolymer of a (meth)acrylate monomer having a straight or branched alkyl group of 1 to 8 carbon atoms and another (meth)acrylate monomer having a straight or branched alkyl group of 1 to 8 carbon atoms in which at least one hydrogen atom is replaced with a hydroxyl group.
In a preferred embodiment of the invention, the crosslinking agent including the peroxide as a main component has a content of 0.01 to 1.0 part by weight, base on 100 parts by weight of the (meth)acrylate (co)polymer.
In a preferred embodiment of the invention, the first pressure-sensitive adhesive layer includes: a pressure-sensitive adhesive that may be produced by crosslinking a composition comprising a (meth)acrylate (co)polymer; and an isocyanate group-containing compound, a silane coupling agent, wherein a crosslinking agent comprising a peroxide as a main component, the isocyanate group-containing compound has a content of 0.005 to 1.0 part by weight, based on 100 parts by weight of the (meth)acrylate (co)polymer, and the silane coupling agent has a content of 0.001 to 2.0 parts by weight, based on 100 parts by weight of the (meth)acrylate (co)polymer.
In a preferred embodiment of the invention, the pressure-sensitive adhesive has a glass transition temperature (Tg) of −70° C. to −10° C.
In a preferred embodiment of the invention, the pressure-sensitive adhesive has a moisture content of 1.0% or less.
In a preferred embodiment of the invention, the laminated film further includes a second pressure-sensitive adhesive layer between the polarizing plate and the retardation film, wherein the second pressure-sensitive adhesive layer includes a pressure-sensitive adhesive that may be produced by crosslinking a composition comprising a (meth)acrylate (co) polymer, a silane coupling agent, and a crosslinking agent comprising an isocyanate group-containing compound as a main component.
A liquid crystal display panel including the laminated film described above and liquid crystal cell is provided in one aspect of the invention.
A liquid crystal display is provided in another aspect of the invention. The liquid display includes the liquid crystal display panel described above.